Blu-ray Disc (BD): high-density optical disc format

Technical characteristics

Blu-ray discs use a blue-violet laser with a wavelength near 405 nm, enabling smaller pits and tracks on the disc surface. Common commercial capacities include a single-layer disc of about 25 GB and a dual-layer disc of roughly 50 GB. Extended variants such as BD-XL support three or four layers, with significantly higher capacities for archival and professional use. Because of the higher density, a dual-layer Blu-ray holds more than five times the data of a standard DVD and many times the storage of a CD.

Formats and compatibility

The Blu-ray family includes several media types and standards: BD-ROM (pre-pressed read-only), BD-R (recordable once) and BD-RE (rewritable). Manufacturers also produced drives and players for computers and consumer electronics; many desktop and laptop personal computer optical drives offered Blu-ray read/write capability. Most Blu-ray players are backward compatible with DVDs and CDs, allowing users to play older discs in many, but not all, players.

History and the 'format war'

Blu-ray was developed by a coalition of electronics, media and computing companies and launched commercially in the 2000s. Its main rival was the HD DVD format; the competition between the two standards is often called the format war. Blu-ray eventually achieved broader industry support and retail adoption, while HD DVD lost major studio and manufacturer backing and was discontinued as a consumer format. The format’s rise was also influenced by prominent adopters such as the PlayStation 3 game console, which used Blu-ray discs for games and media playback.

Uses, codecs and market context

Blu-ray became the standard medium for distributing high-definition movies and television seasons on disc, supporting advanced video codecs such as H.264/AVC and VC-1 as well as high-bitrate audio formats. It has been used for software distribution, archival storage and as a physical format for console games. In recent years physical-disc sales have declined in many markets as streaming and digital distribution gained popularity, but Blu-ray remains important where high-capacity, high-quality local playback or long-term archival storage is required.

Distinctions and notable facts

• Blu-ray discs are named for their blue/violet laser, in contrast to older formats that used a red laser.
• Variants include higher-capacity BD-XL discs and multiple commercial and recordable types (BD-ROM, BD-R, BD-RE).
• The format competed directly with HD DVD during the late 2000s; Blu-ray’s victory consolidated HD optical distribution around one standard.
• Physical discs are region-coded in some releases, but many discs and players are region-free; distribution practices vary by studio and manufacturer.